Among the silicones modified by a polyhydric alcohol derivative, it is possible to indicate a glycerin derivative-modified silicone as an example of a typical material other than a sugar derivative-modified silicone.
Commonly known examples of silicones modified by a glycerin derivative include the compounds disclosed in Patent Documents 1 to 9, and the reaction schemes of such compounds are also well known. Generally, since there are almost no cases in which the introduction reaction of a glycerin derivative to a silicone skeleton proceeds by the chemical equivalent (mole equivalent), the introduction reaction is commonly completed by supplying the glycerin derivative in excess. Therefore, in addition to a glycerin derivative-modified silicone copolymer, which is the product, an unreacted modifier (a glycerin derivative) remains as a residual in the reaction system, resulting in turbidity. Since the glycerin derivative has a high boiling point in most cases, and polyglycerin is a high molecular compound, as such, purification by stripping is not effective. Therefore, it was difficult to obtain a high-purity glycerin derivative-modified silicone on a commercial scale. This is due to not only the fact that stripping at an excessively high temperature causes the degeneration of the product or undesirable side reactions, but also the fact that a technique of stripping impurities having a high boiling point at an even higher temperature is inefficient in an actual production process.
Another technique for increasing the purity of an organo-modified silicone containing a residual organic modifier as an impurity is, for example, an extraction (or precipitation/re-precipitation) separation method utilizing the difference in solubility between impurities and the main component. For example, when the organic modifier is a hydrophilic compound, in an extraction separation method, most of the impurities are first extracted and removed with a hydrophilic solvent (alternatively, the main component is conversely extracted with a lipophilic solvent). However, phase separation in the extraction step ordinarily takes time, and this does not yield clean separation. This results in an increase in waste and a decrease in yield and productivity. In addition, in the case of the glycerin derivative-modified silicone, there are many cases in which the entire system enters an emulsified state and cannot be separated, which leads to poor versatility.
On the other hand, a precipitation and re-precipitation method is a technique of dissolving an organo-modified silicone containing a residual organic modifier in an organic solvent with solubility in both, and precipitating and separating the organo-modified silicone by gradually adding water, for example. Patent Document 10 discloses a high-purity polypropylene glycol-modified organosiloxane polymer obtained by a precipitation and re-precipitation method. However, the total amounts of the organic solvent and water that are used in this method are ten times the amount of the organo-modified silicone each time re-precipitation is performed, and this is repeated three times to obtain a high-purity organo-modified silicone with no impurities. Accordingly, taking into consideration problems such as the low productivity in relation to the number of reactions and the large amount of waste water treatment, application to mass production on a commercial scale is difficult. In addition, when the organic modifier is a polyethylene glycol derivative or a glycerin derivative, the hydrophilicity and surface activity of the corresponding organo-modified silicone are increased, so separation and purification are often difficult with this method.
Patent Document 11 discloses an organosiloxane derivative having a sugar residue but not containing an unreacted starting material, which is obtained by a membrane separation method using a dialysis tube. However, a dialysis time of three days is required to obtain 10 g of a high-purity organo-modified silicone, so this method cannot be considered suitable for mass production on a commercial scale from the perspective of efficiency. In addition, in Patent Document 11, it is stated that the purification of the organopolysiloxane derivative is also possible by column chromatography. Patent Document 4 discloses a glyceryl ether-modified silicone purified by a silica gel column. However, column chromatography requires the circulation of a large amount of a solvent in order to obtain a high-purity organo-modified silicone, and there are many problems with production on a commercial scale, such as the apparatus design, the recovery of the waste solvent, the removal of the solvent from the recovered solution, and low productivity.
Patent Document 12 discloses a purification method for an alkyl glyceryl polysiloxane derivative by means of ultrafiltration utilizing a diafiltration method. However, since the pore diameter of ultrafiltration is small and the film tends to become obstructed in a short amount of time, ultrafiltration must be performed after diluting an organo-modified silicone containing an organic modifier around ten times with a volatile solvent such as hexane. Therefore, there are problems such as the removal of the solvent from the filtrate, low productivity, and operator safety.
Patent Document 7 proposes a method for producing a branched polyglycerol-modified silicone obtained by adding/graft polymerizing a silicone having at least one functional group selected from the group consisting of hydroxy groups, carboxy groups, amino groups, imino groups, mercapto groups, and epoxy groups, with 2,3-epoxy-1-propanol in the presence of an acidic or basic catalyst. With this method, however, the siloxane backbone breaks during graft polymerization, and as a result, at least two components having different properties tend to be produced as copolymers, and there are many problems from the perspectives of quality and the purification step, and thus, it is difficult to obtain a high-purity polyglycerin-modified silicone in a stable manner on a commercial scale.
In addition, Patent Document 13 discloses a hydrogenation treatment for the glycerin-modified polysiloxane, and an acid treatment following the hydrogenation treatment, in Example 5, as a purification method of a modified silicone compound having a branched polymer made of a hydrophilic group. However, this technique is a deodorizing technique by which the unsaturated group portion of the residual organic modifier, which is the source of odorization of the modified silicone composition, is stabilized by hydrolysis and the hydrogenation treatment, and a high-purity glycerin-modified silicone is not obtained. In this technique, the excess glycerin derivative changes the structure thereof and continues to remain in the composition.
Recently, Patent Document 8 has proposed a novel alternating copolymer of organopolysiloxane with glycerin derivative, and suggests that a high molecular weight polyglycerin-modified silicone can be obtained without the problem of white turbidness, and the like, caused by the unreacted starting material. However, it is clear from the chemical structure that this compound has a hydrophilic group portion incorporated on its backbone. As a result, this copolymer has properties completely different than those of conventional general-use hydrophilic silicones such as polyether-modified silicone and the like and, therefore, a high level of technical skill is necessary to stably compound this copolymer in delicate formulations such as cosmetic products and the like, leading to the problem of the field of use being limited.
In such a situation, in Patent Document 14, the present inventors disclose a novel organopolysiloxane containing a hydrophilic group, which is easy to produce and incurs almost no phase separation or sedimentation of unreacted starting material and the like after production, and is chemically stable and has excellent practicality, and a method for producing the same. In particular, they propose that this organopolysiloxane be used as a surfactant, powder treatment agent, and surface treatment agent that can be advantageously used in the field of cosmetics. Moreover, in Patent Document 15, the present inventors disclose a novel liquid organopolysiloxane having flowability at least at 100° C., having a silicon-bonded glycerin derivative group, and also having a crosslinked structure including a carbon-silicon bond in the crosslinking part, and a method for producing the same. At the same time, they propose an external use preparation or cosmetics having an excellent emulsion stability without the inclusion of a compound containing a polyoxyethylene structure, which conforms to the world-wide trend of improving the overall configuration of a product for the end consumer, such as cosmetic products, etc. including the liquid organopolysiloxane, to a PEG-FREE formulation. In addition, the present inventors examine the usage, structure, functions, etc. of these novel materials, and disclose the details in Patent Documents 16 to 23.
In Patent Documents 14 to 23, a production example of not only the glycerin derivative-modified silicone invented by the present inventors, but also of the glycerin derivative-modified silicone based on the prior techniques has been reported as a comparison product. However, most of the compositions containing the glycerin derivative-modified silicone at the point of time when the reaction step ended, except for those for which the hydrogenation treatment is performed, have a milky white to grayish brown opaque appearance. Moreover, there are also case examples of attempts made to reduce the residual glycerin derivative, which is the cause of turbidity, by filtering the opaque composition, however, there are cases in which a translucent appearance is obtained, or conversely, there are also cases in which the turbidity is not removed at all, and as such there has been no known technique of increasing the purity of a glycerin derivative-modified silicone composition that is practical and clear, and is effective for a wide range of design structures.
For example, in Examples 2 to 7 of Patent Document 22, it has been reported that the glycerin derivative co-modified organopolysiloxane that has a low viscosity and a low HLB is obtained as a transparent liquid by performing the filtration process after removing the low-boiling components following the hydrosilylation reaction. Since these glycerin derivative-modified silicones have an extremely low HLB and low viscosity, the affinity of the residual glycerin derivative starting material in the reaction mixture and the glycerin derivative-modified silicone, which is the product, is extremely poor, and when allowed to stand for a period of one day up to a few days at laboratory scale, two-layer separation occurs, and the residual starting material undergoes sedimentation. Hence, by sampling and filtering out only the phase of the glycerin derivative-modified silicone, which is a supernatant, excellent transparency can be obtained. Therefore, there were problems that the yield was low and certain amount of time was required for production, as well as that the applicable range of the structure was narrow. In addition, there was the problem that since the bulk (height) of the reaction mixture increases during production of a large amount on a commercial scale, the time taken until two-layer separation increases significantly as compared to the laboratory scale, which makes it difficult to filter only the supernatant liquid.
As described above, until now, there has been almost no known effective method for producing a liquid high-purity glycerin derivative-modified silicone or a composition containing the same in a stable manner on a commercial scale. Further, there has also been no known technique of increasing the purity of a liquid glycerin derivative-modified silicone which can be applied regardless of the type of the glycerin modifier and can reasonably cope with production on a commercial scale. Therefore, there has been a demand for the development of a high-purity glycerin derivative-modified silicone having low turbidity that is stable while being in liquid form, or a composition thereof, which is easy to produce and incurs almost no phase separation or sedimentation of unreacted starting material or the like after production, and a method for producing the same.